udhcp client (udhcpc) -------------------- The udhcp client negotiates a lease with the DHCP server and notifies a set of scripts when a leases is obtained or lost. command line options ------------------- The command line options for the udhcp client are: -c, --clientid=CLIENTID Client identifier -H, --hostname=HOSTNAME Client hostname -h, Alias for -H -F, --fqdn=FQDN Client fully qualified domain name -f, --foreground Do not fork after getting lease -b, --background Fork to background if lease cannot be immediately negotiated. -i, --interface=INTERFACE Interface to use (default: eth0) -n, --now Exit with failure if lease cannot be immediately negotiated. -p, --pidfile=file Store process ID of daemon in file -q, --quit Quit after obtaining lease -r, --request=IP IP address to request (default: none) -s, --script=file Run file at dhcp events (default: /etc/udhcpc/default.script) -v, --version Display version If the requested IP address cannot be obtained, the client accepts the address that the server offers. udhcp client scripts ------------------- When an event occurs, udhcpc calls the action script. udhcpc never does any configuration of the network interface itself, but instead relies on a set of scripts. The script by default is /etc/udhcpc/default.script but this can be changed via the command line arguments. The three possible arguments to the script are: deconfig: This argument is used when udhcpc starts, and when a leases is lost. The script must put the interface in an up, but deconfigured state, ie: ifconfig $interface 0.0.0.0. bound: This argument is used when udhcpc moves from an unbound, to a bound state. All of the paramaters are set in enviromental variables, The script should configure the interface, and set any other relavent parameters (default gateway, dns server, etc). renew: This argument is used when a DHCP lease is renewed. All of the paramaters are set in enviromental variables. This argument is used when the interface is already configured, so the IP address, will not change, however, the other DHCP paramaters, such as the default gateway, subnet mask, and dns server may change. nak: This argument is used with udhcpc receives a NAK message. The script with the deconfig argument will be called directly afterwards, so no changes to the network interface are neccessary. This hook is provided for purely informational purposes (the message option may contain a reason for the NAK). The paramaters for enviromental variables are as follows: $HOME - The set $HOME env or "/" $PATH - the set $PATH env or "/bin:/usr/bin:/sbin:/usr/sbin" $1 - What action the script should perform interface - The interface this was obtained on ip - The obtained IP mask - The number of bits in the netmask (ie: 24) siaddr - The bootp next server option sname - The bootp server name option boot_file - The bootp boot file option subnet - The assigend subnet mask timezone - Offset in seconds from UTC router - A list of routers timesvr - A list of time servers namesvr - A list of IEN 116 name servers dns - A list of DNS server logsvr - A list of MIT-LCS UDP log servers cookiesvr - A list of RFC 865 cookie servers lprsvr - A list of LPR servers hostname - The assigned hostname bootsize - The length in 512 octect blocks of the bootfile domain - The domain name of the network swapsvr - The IP address of the client's swap server rootpath - The path name of the client's root disk ipttl - The TTL to use for this network mtu - The MTU to use for this network broadcast - The broadcast address for this network ntpsrv - A list of NTP servers wins - A list of WINS servers lease - The lease time, in seconds dhcptype - DHCP message type (safely ignored) serverid - The IP of the server message - Reason for a DHCPNAK tftp - The TFTP server name bootfile - The bootfile name additional options are easily added in options.c. note on udhcpc's random seed --------------------------- udhcpc will seed its random number generator (used for generating xid's) by reading /dev/urandom. If you have a lot of embedded systems on the same network, with no entropy, you can either seed /dev/urandom by a method of your own, or doing the following on startup: ifconfig eth0 > /dev/urandom in order to seed /dev/urandom with some data (mac address) unique to your system. If reading /dev/urandom fails, udhcpc will fall back to its old behavior of seeding with time(0). signals accepted by udhcpc ------------------------- udhcpc also responds to SIGUSR1 and SIGUSR2. SIGUSR1 will force a renew state, and SIGUSR2 will force a release of the current lease, and cause udhcpc to go into an inactive state (until it is killed, or receives a SIGUSR1). You do not need to sleep between sending signals, as signals received are processed sequencially in the order they are received. compile time options ------------------- options.c contains a set of dhcp options for the client: name[10]: The name of the option as it will appear in scripts flags: The type of option, as well as if it will be requested by the client (OPTION_REQ) code: The DHCP code for this option